1. Field of the Invention
This invention pertains to a digitally-controlled telephone switching system for an answering system covering a wide geographic area based on a series of remote and central trunk concentrators which minimize and optimize the number of trunk lines required in the operation of a telephone answering service. The trunk concentrators enable the telephone answering system, under computer control, to connect an available free path from the input side to the output side and eventually to a computer terminal of the operator who will answer the call.
The system of the present invention is designed to operate in a computer-controlled telephone answering system serving subscribers over a wide geographic area and linked to numerous telephone company central offices. It includes a remote site concentrator which reduces the number of trunk lines necessary to connect subscriber telephones to a central answering service office and includes special purpose digital logic for switching control, command verification, ring detection and data communications to and from the central answering service office, thus functioning as a remote site special purpose computer; a central site concentrator which further reduces the number of trunks required for connections within the central answering service center to operator positions in a non-blocking manner; a central computer for control of the system and storage of messages; and an operator console including a computer terminal for operator answering of individual calls processed by the system.
2. Description of the Prior Art
Telephone answering systems are well known in the prior art and need not be described specifically here.
The prior art does disclose, however, a number of switching systems for minimizing the number of trunk lines required between a telephone company central office and the switchboard of a telephone answering service. U.S. Pat. No. 3,002,054, as an example, discloses a trunk concentrator for telephone answering service for installation and operation in a telephone company central office which enables a reduction in the number of trunks required to connect each subscriber line to a remote telephone answering service. It is uncertain, however, what level of reduction occurs within such a system and whether the concentrator can be economically utilized in large scale answering systems covering a wide geographic region and numerous telephone company central offices. It also appears that this system requires a conventional switchboard and conventional operator positions, a limitation not necessitated in the system of the present invention.
The system of the present invention is based upon a number of statistical factors observed in the study of telephone answering systems. A telephone answering service has a relatively large number of subscribers whose telephone lines are connected to the answering service lines at a telephone company central office. For every 512 subscriber lines so connected, only a small percentage will be in use at any one time. For every 512 subscriber lines served by a telephone answering service, statistics indicate that only eight of said lines are active at peak times, and as few as none to two are active in non-peak times. However, in a conventional system, there must be positions on an answering service switchboard for all 512 lines. With some effort, an operator can reach to the boards at either side of her position to cover another 100 or 200 lines, if she is not busy. Present telephone answering systems, however, provide no way to direct an incoming call on a given subscriber line to any operator position which is not busy. These calls must be directed to the operator position on the specific switchboard to which the subscriber's line is connected, regardless of the current workload of the operator. This results in a considerable lack of flexibility and unnecessary operating costs for a telephone answering service.
The system of the present invention is designed to minimize the number of trunks required to service the subscribers of a telephone answering service through the use of at least two trunk concentrators which are under the control of a computer. The first type of trunk concentrator, of which there may be more than one, is located at a remote site, preferably adjacent to a telephone company central office serving individual subscribers. For each 512 subscriber lines coming into each remote site, from a single telephone company central office, there is an analog switching matrix which will switch any one of the 512 incoming lines to any one of eight outgoing trunks which transmit signals to the answering service central location. Each remote site also has the equivalent of a special purpose, control minicomputer to control and verify the operation of the analog switching matrices, a memory to hold temporarily command messages for forwarding to the central location of the answering service, and digital logic for ring detection, switch control and message verification.
Each remote site of the answering service is connected to a central site at which the calls are actually answered by operators. For every 128 trunks reaching the central site, there are up to sixty-four operator positions, each of which is able to answer any one of the 128 trunks coming into the central site. To accomplish this, a central site concentrator is utilized which is a 128 by 64 analog switching matrix under the control of a central site computer. Each operator position is basically a computer input-output terminal with a keyboard, a cathode ray tube (CRT) display, and a memory and control unit. The central site computer, in addition to a control program for the entire system, also contains within its memory the pertinent information required by an operator to answer each incoming call. As the computer recognizes a call to be answered, it determines by the table lookup, which operator position is free to answer the call and sends the pertinent answering information to the operator terminal to which it will direct the call. After the operator receives the call and takes the caller's message, the operator will key the incoming message into the computer where it will be stored until the subscriber calls for his messages. In this fashion, the system minimizes the chance of operator error in answering calls, in taking messages, and in giving messages to the subscriber. It also maximizes the use of operator labor by providing a computer based retrieval system rather than a manual retrieval system.
The present embodiment of the system, as described herein, accomodates up to 1,024 subscriber lines at each remote site, which lines are concentrated to as many as sixteen trunk lines going to the central site. Each central site can handle as many as 128 trunk lines from various remote sites, thus eight remote sites serving a total of 8,192 subscriber lines, as illustrated in the drawings; any one of which subscriber lines can be answered at any operator terminal; a flexibility which is impossible to achieve in any other telephone answering system. The number of remote sites is limited by the 128 inputs to the central control concentrators.